1. Technical Field
The technical field relates to liquid crystal display (LCD) devices, and more particularly, to a method for driving an LCD device, in which the LCD device is driven in a fringe field switching (FFS) mode during a frame frequency period to obtain a wide viewing angle while sub-frames divided from a frame are sequentially driven in both an FFS mode and a viewing angle control (VAC) mode during the frame frequency period to obtain a narrow viewing angle, thereby resulting in that a narrow viewing angle is obtained in view of time average.
2. Discussion of the Related Art
Recently, active matrix LCD devices have become widely used in flat TVs, portable computers, monitors in accordance with their developing performance.
Generally used among the active matrix LCD devices is the twisted nematic (TN) mode LCD device. The TN mode LCD device drives a liquid crystal director twisted at an angle 90° by applying a voltage to electrodes arranged on two substrates.
The TN mode LCD device provides excellent contrast and excellent color reproduction but has a narrow viewing angle.
To solve such a problem relating to the narrow viewing angle of the TN mode LCD device, a fringe field switching (FFS) mode LCD device has been developed, in which a relative electrode and a pixel electrode are formed of transparent conductive materials. The distance between the relative electrode and the pixel electrode is then maintained at a narrow range to drive liquid crystal molecules using a fringe field formed between the relative electrode and the pixel electrode.
FIG. 1 is a sectional view illustrating the related art FFS mode LCD device.
First, as shown in FIG. 1, a TFT array substrate 11 of the related art FFS mode LCD device includes gate lines (not shown) and data lines 15 formed of opaque metal, orthogonally crossing each other to define sub pixels, common lines (not shown) arranged in parallel with the gate lines, thin film transistors switching on/off a voltage at crossing portions of the gate and data lines, and relative and pixel electrodes 24 and 17 formed of a transparent conductive material, insulated by an insulating layer, and overlapped with each other within pixel regions. At this time, the relative electrodes are in contact with the common lines.
In more detail, each relative electrode 24 is formed of a plate type transparent conductor within the pixel region. The pixel electrodes 17 are forked along the data lines, and slits 60 are respectively formed between the forked pixel electrodes. At this time, a Vcom signal is transmitted to the relative electrode 24 and a pixel signal passing through the thin film transistor is transmitted to the pixel electrode 17, so that a fringe field occurs between the relative electrode 24 and the pixel electrode 17.
Each of the slits 60 has a width of 2 μm to 6 μm. Liquid crystals are driven by the fringe field formed between the pixel electrode 17 and the relative electrode 24. In other words, the liquid crystals initially aligned by rubbing in case of no voltage are rotated by the fringe field to transmit light.
Additionally, a color filter array substrate 21 is bonded to the TFT array substrate 11 by interposing a liquid crystal layer 31 in between. The color filter array substrate 21 includes R/G/B color filter layers 23 arranged at constant intervals to display colors, and a black matrix layer 22 that serves to divide R/G/B cells from one another and shield light.
The respective color filter layers 23 are formed to allow each sub-pixel to have one color. The sub-pixels having R/G/B colors are independently driven, and a color of one pixel is displayed by combination of the sub-pixels.
The R/G/B color filter layers 23 are arranged depending on their arrangement methods such as a stripe arrangement, a mosaic arrangement, a delta arrangement, and a quad arrangement. The R/G/B color filter layers 23 are variously arranged depending on the size of an LCD panel, a shape of the color filter array, and color arrangement.
The aforementioned LCD device is driven in such a manner that image signals are applied to the data lines and electric pulses are applied to the gate lines in a scan manner. In order to improve picture quality, one gate pulse voltage is applied to each gate line in a sequential driving manner using a gate scan input device. In this way, if the gate pulse voltages are all applied to the gate lines, one frame is completed.
In other words, if the gate pulse voltage is applied to the nth gate line, all the thin film transistors connected with the gate line to which the gate pulse voltage is applied are turned on. Image signals of the data lines are stored in a liquid crystal cell and a storage capacitor through the turned-on thin film transistor.
Therefore, the liquid crystal molecules in the liquid crystal cell are rearranged in accordance with the image signals stored in the liquid crystal cell and the voltages of the image signals to allow light of a backlight to pass through the liquid crystal cell, thereby displaying a desired screen.
Although a related art FFS mode LCD device has a wide viewing angle, a narrow viewing angle is required to prevent personal information from being exposed to other persons. Thus, a viewing control layer or sub-pixels for controlling a viewing angle may additionally be provided. However, there often is a low viewing control effect, and the process of forming the sub-pixels for controlling a viewing angle and the driving method for controlling the sub-pixels are complicated.
Hence, the driving method of controlling the viewing angle of the sub-pixels is complicated because a new electrode layer as a viewing control layer must be added and then a signal must be applied to the new electrode layer.